This invention relates to a polymer which may be utilized for a material for an artificial organ or a surface modifier for a high molecular material, a diester monomer employed as a starting monomer for the polymer, a water-containing soft contact lens, and a processing solution for the contact lens.
There have hitherto been known a variety of compounds, such as N-vinyl pyrrolidone, 2-hydroxy ethyl methacrylate or (meth)acrylic acid, as water-soluble monomers. Polymers obtained on polymerizing the water-soluble monomers are employed in bio-related fields, such as contact lenses or cosmetics. However, the aforementioned polymers suffer from drawbacks such as inferior mechanical strength or inadvertent adsorption of protein and lipid, such that these polymers are not satisfactory as a material directly related with a living tissue, such as a material for artificial organs.
Thus, a demand has been raised for a material having a functional relationship with a living body, and consequently a variety of monomers exhibiting biocompatibility have been proposed. As a monomer exhibiting biocompatibiity, 2-methacryl phosphorylcholine, which is a monomer having a structure similar to that of phospholipid, a main constituent of a membrane of a living body, has been proposed in Japanese Laid-open Patent Application No. 54-63025 (1979). Attempts have been made for applying a polymer produced on polymerizing 2-methacryl phosphorylcholine to artificial organs, contact lenses or artificial blood vessels.
However, the above-mentioned 2-methacryl phosphorylcholine is susceptible to polymerization and poor in thermal stability because its polymerizable group is a methacrylic group. Besides, limitations are imposed on the kinds of comonomers which may be employed for copolymerization.
On the other hand, a water-containing soft contact lens has high affinity to an eye and may be fitted comfortably as compared to a non-water-containing hard contact lens containing methyl methacrylate or siloxanyl alkyl methacrylate as main monomer components.
As the water-containing soft contact lens, there has been known a contact lens which is composed mainly of 2-hydroxyethyl methacrylate and which, despite its moisture content of not higher than 40%, is superior in mechanical strength and machinability. Recently, a high water content soft contact lens has been developed with a view to continued attachment to the eye by raising the moisture content of the lens material. For example, there has been known a soft contact lens which is mainly composed of N-vinyl pyrrolidone copolymerized with methyl methacrylate, 2-hydroxyethyl methacrylate or methacrylic acid.
However, the soft contact lens composed mainly of N-vinyl pyrrolidone suffers from a number of drawbacks, such as susceptibility to deposition of dust and dirt, decreased mechanical strength, difficulties in lens processing by machining and grinding, and change to yellowish color caused by repetition of sterilization processes indispensable to soft contact lenses. On the other hand, although the soft contact lens composed mainly of 2-hydroxyethyl methacrylate, is free from these drawbacks, saturation of the lens with water takes much time because of the low water content of the lens, while the lens also suffers from production-related problems, such as fluctuations in the moisture content.
In general, a soft contact lens suffers from hygienic problems caused by deposition of protein and lipid or bacterial proliferation and a problem that a rise in the moisture content leads to a decreased mechanical strength. It is therefore usually necessary to maintain the contact lens in a sanitary condition by sterilization by boiling or treatment with a disinfectant or a rinsing solution.
The contact lens may be classified into a water-containing contact lens and a non-water-containing contact lens. The latter may be classified into a hard contact lens and a soft contact lens. The non-water-containing contact lens is superior to the water-containing contact lens in respect of stability of the lens material and ease in maintenance. There has so far been known such non-water-containing contact lens composed mainly of methyl methacrylate or formed of silicon rubber. Recently, a high oxygen permeable type hard contact lens composed mainly of silyl-based methacrylate or fluorine-based methacrylate for further reducing adverse effects on the eye, has been put to practical utilization.
However, the non-water-containing contact lens suffers from drawbacks that it has poor fitting feel because the lens surface exhibits hydrophobicity and the lens has adverse effects on the intraocular nerves. Above all, the high oxygen permeating hard contact lens exhibits strong hydrophobicity because of the content of a large quantity of silicon and fluorine, and hence is poor in tight fitting to the eye so that it is inferior in fitting feel and susceptible to deposition of protein or lipid.
For affording hydrophilicity to the hydrophobic surface of the contact lens, the contact lens is processed with plasma or with chemical substances, such as acidic or basic agents. However, such method suffers from a drawback that the lens surface can not be maintained in the hydrophilic condition with ease, while the contact lens tends to be modified by chemical processing and the processing operation tends to be complicated.
For affording hydrophilicity to the contact lens surface, it has also been proposed in Japanese Patent Publication No. 48-37910 (1973) to dip the contact lens in a solution containing a water-soluble polymer, such as polyvinyl alcohol, hydroxyethyl cellulose or polyvinyl pyrrolidone or the like. However, this method has a drawback that limitations are imposed on the degree of hydrophilicity depending on the contact lens type, while it is impossible to prevent deposition of protein and lipid satisfactorily.